Communication terminal

ABSTRACT

A terminal designed for communication with contactless-type data carriers with two different carrier frequencies has two resonant circuits (I, II) for one and the other carrier frequency. Both resonant circuits (I, II) work with one and the same antenna (A) and one capacitor (C 1,  C 3 ) in each case. In the resonant circuit (II) for low carrier frequency a coupling inductance coil (L) is provided between the capacitor (C 3 ) and the antenna (A).

[0001] This invention relates to a terminal for data communication withcontactless-type data carriers, having a transceiver electronics withtwo resonant circuits with an antenna and capacitor for radiatingelectromagnetic waves with different carrier frequencies.

[0002] The data carriers are formed as transponders. After activation bythe terminal's electromagnetic field, data stored in the data carriercan be read out and changed if necessary.

[0003] Contactless-type data carriers, for example contactless-typesmart cards, are used for a great variety of applications, for examplefor the use of public transport systems, as electronic purses, healthinsurance ID cards and the like. Since the number of smart cards that aperson carries is in general increasing constantly, it is desirable tohave a multifunctional data carrier that can be employed for as many asapplications as possible.

[0004] Higher-frequency transponders are superior to transponders with alower carrier frequency, in particular with respect to the data transferrate. On the other hand, high-frequency transponders lead to a largefrequency bandwidth at a high data transfer rate. It is thereforedesirable to be able to use a high or low carrier frequencyalternatively for communication between the terminal and the datacarriers depending on the application.

[0005] While the choice of carrier frequency used to be largely free,now the carrier frequency, allowable frequency bandwidth andtransmitting energy radiated by the terminal are fixed by governingregulations. For example, a carrier frequency of 13.56 MHz is stipulatedby the ISO standard.

[0006] On the other hand, there are still numerous data carriers thatwork with another, usually much lower carrier frequency. For example,for access entitlement to ski lifts one uses data carriers with acarrier frequency of 120-125 kHz integrated e.g. into watches, clothesor the like. If communication between access terminal and data carriershows access entitlement, the access terminal emits an enabling signal,for example to release a blocking apparatus like a turnstile.

[0007] To permit terminals to communicate with data carriers ofdifferent carrier frequencies, e.g. both with 13.56 MHz data carriersand with 125 kHz data carriers, each prior art terminal has two resonantcircuits, one resonant circuit with a small antenna for low carrierfrequency and one resonant circuit with a large antenna for high carrierfrequency (DE 198 31 767). This involves high additional expenditure andspace problems. Moreover, the antennas can influence each other.

[0008] DE 196 51 719 A1 discloses a wireless transceiver system forexample for interrogating IC cards which has primary and secondarycircuit devices and thus a terminal for communication withcontactless-type data carriers. The secondary device includes tworesonant circuits having different resonant frequencies. Theelectromagnetic oscillations to be emitted are radiated via theparticular resonant circuit coil.

[0009] According to WO 94/03982 A1, two frequencies are used foridentification. DE 39 22 977 C2 discloses a trimming circuit whereinelectromagnetic oscillations of different frequency positions areradiated via a single antenna, the single resonant circuit beingadjusted in its frequency position by connection or disconnection ofindividual capacitances.

[0010] The problem of the invention is to substantially reduce theexpenditure and the space required for a terminal capable ofcommunicating contactlessly with data carriers with two different datatransfer carrier frequencies.

[0011] This is obtained according to the invention by the terminalcharacterized in claim 1. The subclaims render advantageous embodimentsof the inventive terminal.

[0012] According to the invention one uses a single, common antenna forboth resonant circuits, i.e. both for the high-frequency and for thelow-frequency resonant circuit of the terminal. This considerablyreduces the expenditure and the space required. It is furtheradvantageous that there is no longer any mutual influencing of severalantennas.

[0013] A coupling inductance coil is provided according to the inventionin the resonant circuit for low carrier frequency between its capacitorand the antenna. Said coil forms a high A.C. resistance for high carrierfrequency but a small one for low carrier frequency, so that only theresonant circuit for high carrier frequency communicates with datacarriers designed for high carrier frequency.

[0014] The ratio of the A.C. resistance of said coil corresponds exactlyto the carrier frequency ratio of the two resonant circuits(X_(L)=2π·f·L). That is, the resistance of the coil is e.g. about 110times greater at a high carrier frequency of 13.56 MHz compared to a lowcarrier frequency of 125 kHz. In general, the ratio of high carrierfrequency to low carrier frequency should be at least 10, preferably atleast 50.

[0015] In order to guarantee that only the resonant circuit for lowcarrier frequency communicates with data carriers designed for lowcarrier frequency, at least one capacitor is preferably provided betweenthe transceiver electronics of the terminal and the resonant circuit forhigh carrier frequency. Said capacitor forms together with the capacitorin the resonant circuit for high carrier frequency a high resistance forlow carrier frequency but a low resistance for high carrier frequency,so that only the resonant circuit for low carrier frequency communicateswith data carriers designed for low carrier frequency.

[0016] At the same time, the capacitor (C2) between the transceiverelectronics and the resonant circuit for high carrier frequency formstogether with the resonant circuit capacitor (C1) an adapter circuit forthe driver stage, thereby avoiding reflection and parasitic powerradiation. The transceiver electronics of the terminal is connected withthe antenna with a coax cable with a corresponding characteristicimpedance.

[0017] Preferably, the resonant circuit for high carrier frequency hasat least one shunt resistor in order to permit adjustment of the qualityof said resonant circuit.

[0018] According to the invention, the two resonant circuits can beactivated for communication alternatingly with a multiplexer forexample. It is even also possible to activate both resonant circuits forcommunication simultaneously.

[0019] In the following, the invention will be explained in more detailby way of example with reference to the enclosed drawing showing a basicwiring of the two resonant circuits.

[0020] Thus, resonant circuit I of the terminal (not shown) for the highcarrier frequency of e.g. 13.56 MHz includes antenna A and capacitor C1.The transceiver electronics (not shown) of the terminal is attached atP1, i.e. connected with resonant circuit I via capacitor C2.Furthermore, resonant circuit I has shunt resistor R for determining thequality of the resonant circuit.

[0021] Second resonant circuit II for the low carrier frequency of e.g.125 kHz likewise includes antenna A and capacitor C3. Antenna A is thuscommon to both resonant circuits I and II.

[0022] Resonant circuit II further includes inductance coil L betweencapacitor C3 and antenna A. The transceiver electronics is attached toresonant circuit II at P2. The high and low carrier frequencies of forexample 13.56 MHz and 125 kHz are fed to resonant circuits I and II bycorresponding harmonic oscillators.

1. A terminal for communication with contactless-type data carriers,having a transceiver electronics with two resonant circuits with anantenna and a capacitor for radiating electromagnetic waves withdifferent carrier frequencies, characterized by a common antenna (A) forboth resonant circuits (I and II), and at least one capacitor (C1, C3)in each resonant circuit (I, II), a coupling inductance coil (L) beingprovided in the resonant circuit (II) for low carrier frequency betweenthe capacitor (C3) and the antenna (A).
 2. A terminal according to claim1, characterized in that the transceiver electronics is attached to theresonant circuit (I) for high carrier frequency via at least onecapacitor (C2).
 3. A terminal according to claim 1, characterized inthat the resonant circuit (I) for high carrier frequency has at leastone shunt resistor (R) for adjusting the quality of the resonantcircuit.
 4. A terminal according to any of the above claims,characterized in that the ratio of high carrier frequency to low carrierfrequency is at least 10:1.
 5. A terminal according to any of the aboveclaims, characterized in that both resonant circuits (I and II) areactivated for communication alternatingly.
 6. A terminal according toany of claims 1 to 4, characterized in that both resonant circuits (Iand II) are activated for communication simultaneously.